The present invention relates generally to aperture and lens mechanisms for cameras, and more particularly to such mechanisms wherein the lens can be rotated to focus and the aperture can be varied.
Many cameras have an aperture system that provides a method of controlling the amount of light that hits the light sensitive device (film, CCD, etc.). In most simple optical systems, this aperture should be a fixed distance from the lens. If the lens is moved relative to the aperture plane, then some optical degradation occurs (loss of resolution). Typically, the aperture is on a blade that rotates or translates into the path of the optical system. The plane of aperture blade is usually in a fixed plane relative to the rest of the camera and the lens system moves closer or farther away from this plane as the lens is focused. In most camera systems, this motion of the lens relative to the aperture plane is very small and an insignificant amount of optical degradation occurs. However, if the distance variation between the lens and the aperture plane becomes too large, the optical degradation can be significant. For example, in some cameras, there is a desire to have a very close focus distance such as 2 inches. For a lens with a focal length of 6.2 mm, the lens must translate approximately .86 mm relative to the sensor to achieve a focus range of 2 inches to infinity. If the aperture is in a fixed plane, then the lens to aperture distance variation will be 0.86 mm. This amount of lens to aperture variation can result in a significant optical degradation (loss of resolution).
As a lens in a camera system moves relative to the image plane in order to achieve focus it typically is also rotating (on a set of three ramps or on a threaded interface). If an aperture were to move with the lens for the reasons described above, then it too would be rotating. This can be a problem if the means for selecting the aperture is to be done manually since the aperture select button (mechanical user interface button) needs to be in a fixed position relative to the product whereas the aperture blade is rotating relative to the product.
Accordingly, a need continues to exist for an aperture and lens mechanism that avoids these problems.
The need is met according to the invention, by providing an aperture and lens mechanism for a camera, that includes a rotatably mounted lens barrel supporting a lens and moveable in a direction parallel to the optical axis of the lens in response to rotation; an aperture support mounted for movement parallel to the optical axis of the lens and spring biased into contact with the lens barrel for movement therewith; and an aperture blade defining an aperture, the aperture blade being mounted on the aperture support for movement between a first position where the aperture is centered on the optical axis of the lens and a second position away from the optical axis of the lens.
The aperture and lens mechanism of the present invention has the advantage that the aperture stays in relative position to the lens to minimize optical degradation which can occur if focus extremes are great. Another advantage of this concept is that the location of the aperture can be located more accurately to the lens (centerline of aperture to optical axis). This is important because the greater the distance between the centerline of the aperture and the optical axis, the greater the degradation of the optical system. If the lens does not directly locate the aperture plate, then there is a greater tolerance build-up that can adversely affect the lens to aperture alignment and therefore the optical performance.